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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 16 |
| 4 | 81 |
| 5 | 301 |
| 6 | 1451 |
| 7 | 6231 |
| 8 | 29891 |
| 9 | 137731 |
| 10 | 666976 |
| 11 | 3193026 |
| 12 | 15658831 |
| 13 | 76719891 |
| 14 | 380788006 |
| 15 | 1894818776 |
| 16 | 9502977851 |
| 17 | 47822585931 |
| 18 | 241944876266 |
| 19 | 1228151169656 |
| 20 | 6258922649451 |
| 21 | 31992657321551 |
| 22 | 164040821525031 |
[1,1,6,16,81,301,1451,6231,29891,137731,666976, 3193026,15658831,76719891,380788006,1894818776, 9502977851,47822585931,241944876266,1228151169656, 6258922649451,31992657321551,164040821525031] |